Method of Accelerating the Growth and Development of Trees and Shrubs Via Enhanced Root Development

ABSTRACT

A method and container for developing seedlings includes germinating the seeds and air pruning the seedlings to a depth of about 3 inches.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/599,819, filed Jan. 19, 2015, which is a continuation ofU.S. patent application Ser. No. 13/913,226, filed Jun. 7, 2013, whichis a continuation of U.S. patent application Ser. No. 13/568,056, filedAug. 6, 2012, now U.S. Pat. No. 8,460,677, which is a divisional of U.S.patent application Ser. No. 11/731,997, filed on Apr. 2, 2007, now U.S.Pat. No. 8,236,322, and which is a divisional of Ser. No. 10/216,092,filed Aug. 9, 2002, now U.S. Pat. No. 7,308,775, and which claimspriority from U.S. provisional patent application No. 60/312,593, filedAug. 15, 2001, each of which are incorporated herein by reference intheir entireties.

BACKGROUND OF THE INVENTION Field of the Invention

There is an ever-increasing demand for native hardwoods, but commercialfarming of this class of trees is frustrated by the slow growth of thisclass of trees and the difficulty in transplanting them. Similarly,non-commercial reforestation with hardwoods is frustrated by the slowgrowth and transplantation difficulties. “Traditional” productionmethods for native hardwoods such as Oaks, Hickories, Ash, Nut trees andothers are notoriously slow growing and tend to develop a coarse,carrot-like dominant tap root which makes them very difficult totransplant both in the nursery and especially in out-plantingsituations—where mortality rates often ran as high as 70 percent ormore.

To try and overcome the problems associated with transplantability ofnative hardwoods and other difficult to transplant species, manynurseries began to “root-prune” their plants while in the field one tothree years prior to sale in hopes of developing a “secondary” rootsystem which would give this class of plants a better chance ofsurviving the out-planting process. The major problem associated withroot-pruning in the field is that it not only “shocks” the plantsbecause its root system has been severed but also halts growth andforces the grower to “wait” for another year or more for the root systemto re-develop. Although the process of root pruning in the field greatlyhelped to minimize loss after out-planting, the process was slow, costlyand extended the time a plant must remain in the nursery.

One prior art method of root pruning is disclosed in Huang and Liang,Effects of Air-Pruning on Cutting and Seeding Growth in Container TreePropagation, SNA Research Conference 1987, incorporated herein byreference, pages 134-137.

SUMMARY OF THE INVENTION

This inventions relates to a method of accelerating the growth anddevelopment of trees via an enhanced root system. Generally, the methodof this invention comprises: Selecting seed of the species to be grownfrom trees from the same climate, and preferably the same growingconditions. Sorting the seed is based upon density, size, and/or weight.Placing the seed on the surface of a growing medium. Subjecting the seedto cold stratification in sufficient time to maximize the growing season(time of last frost to time of first frost) upon subsequent transferoutside. Transferring the cold-stratified seed to a greenhouse to beinggermination is about 30 days, subjecting the seedling to air rootpruning at a depth of about 3 inches. Sorting the seedling according toheight and caliper, and transplanting the seedling to bottomlessbands/pots. Growing the seedling in bottomless bands while subjectingthe seedling to a further air root pruning at a depth of about 4¼inches. Hardening of the seedling off, and transplanting the seedlingfor further growth outside as close to the beginning of the growingseason as possible to maximize the growing season and growth potential.

The general method of this invention, without the specific details ofthe invention described and claimed herein, is disclosed in Lovelace,The Root Production Method (RPM) System for Producing Container Trees,The International Plant Propagators' Society Combined Proceedings, Vol.48 (1998), incorporated herein by reference.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a photograph illustrating the grading of seed by density usinga Jesse Aspirator.

FIG. 2 is a photograph illustrating the grading of seed by weight andsize using a Savage Sizer and an Oliver Gravity Table for smaller seed.

FIG. 3 is a photograph showing graded seed of Quercus bicolor. SwampWhite Oak F2 Orchard—large seed 76 per pound, medium seed 100 per poundand small seed 142 per pound. Swamp White Oak F2 Orchard (Special Tree#6) 64 per pound.

FIG. 4 is a photograph illustrating the bottomless flats used for airpruning in accordance with the principles of this invention;

FIG. 5 is a photograph of seed of Quercus bicolor shown on the surfaceof growing media in preparation for cold stratification;

FIG. 6 is a photograph of seeds of other species shown on the surface ofgrowing media in preparation for cold stratification;

FIG. 7 is a photograph of stacks of flats of seeds ready for coldstratification;

FIG. 8 is a photograph showing stacks of flats of seeds in coldstratification;

FIG. 9 is a photograph showing stacks of flats of seeds in coldstratification;

FIG. 10 is photograph showing flats after stratification, placed in agreenhouse on bottomless benches for germination;

FIG. 11 is a photograph showing root radicals beginning to penetrate thebottomless flat;

FIG. 12 is close-up photograph showing root radicals beginning topenetrate the bottomless flat;

FIG. 13 is a photograph showing germinating seedlings of Quercusbicolor;

FIG. 14 is a photograph showing germinating seedlings of Quercus bicolorprior to grading and transplantation for the second air root pruningstep;

FIG. 15 is a photograph showing germinating seedlings of Quercus bicolorduring the step of grading the seedlings by height and caliper resultingin taller individuals with larger caliper.

FIG. 16 is a photograph showing the seedlings transplanted intobottomless bands in flats for the second air-pruning step;

FIG. 17 is a photograph showing the root system of Quercus bicolor after30 days, at the time of transplantation for the second root pruningstep;

FIG. 18 is a photograph showing the root radicals protruding through thebottom of the bottomless bands during the second air root pruning step;

FIG. 19 is a photograph showing container ready for transplantation ofthe seedlings after the second root pruning step;

FIG. 20 is a photograph illustrating the transplantation of seedlingsafter the second air root pruning step;

FIG. 21 is a photograph showing Quercus rubra (Northern Red Oak)seedlings at a height of about 7 feet, 210 days from germination;

FIG. 22 is a photograph showing the root system of the seedlings shownin FIG. 21;

FIG. 23 is a photograph showing mycorrhizae on the roots of seedlingsgrown in accordance with the principles of this invention;

FIG. 24 is a photograph showing the development of a root system of anoak tree after four years;

FIG. 25 is a photograph showing the development of root system of an oaktree after four years:

FIG. 26 is a photograph showing the early fruiting (3 years) of Quercusbicolor grown in accordance with the principles of this invention:

FIG. 27 is a photograph showing the early fruiting (3 years) of Quercusbicolor grown in accordance with the principles of this invention;

FIG. 28 is a photograph showing the early fruiting (3 years) of Quercusmuehlenbergii grown in accordance with the principles of this invention;

FIG. 29 is a photograph showing a bottomless flat with ⅜ in. openingsfor air pruning used in Step 1;

FIG. 30 is a photograph of a bottomless pot measuring 3 9/16 in.×3 9/16in.×4¼ in. deep used in Step 1;

FIG. 31 is a photograph of pecan seedlings new system of air pruning at3 in. depth on left showing better growth at time of selection andgrading;

FIG. 32 is a photograph showing the difference between air root pruningat 2 inches (left) versus at 3 inches (right);

FIG. 33 is a photograph of Pecans seeded in an air pruning flat;

FIG. 34 is a photograph of European Ash root 160 days from plantinggrown in accordance with the principles of this invention;

FIG. 35 is a photograph of European Ash root 160 days from plantinggrown with conventional method;

FIG. 36 is a photograph of the root system of two or three year oldPecan grown with convention methods;

FIG. 37 is a photograph of two air pruned 75 day old Pecan grown inaccordance with the principles of this invention.

DETAILED DESCRIPTION OF THE INVENTION

The method of the present invention involves consideration of seedselection, including seed origin (provenance, density, and size). Itfurther involves consideration of seed handling includingstratification, timing of germination to extend growing season,technique (depth) of seeding. It further involves air pruning,preferably in two steps using air as a means of root pruning to enhancethe development of a dense fibrous root mass. It further involvesgradation for uniformity of stock and to reduce transplanting losses.Lastly, the method involves selection of growing media, includingfertilizer, consideration of air space, wetting agents, and components.The method of the present invention accelerates rate of growth, andinduces early flowering and fruiting.

Seed selection is an important component in the acceleration of treegrowth. Special attention is provided to assure seed is selected fromsuperior individual parents, showing outstanding phenotype, typical ofthe particular specie or variety of tree. Attention also must be focusedon the climate zone of origin, including attitude and locations withinits native geographical range, normally referred to as “provenance”.Within a given provenance, seed is selected based on environmentalconditions of the final location. It is desirable to select seed fromthe same species growing in the same environmental conditions, e.g., aflood plain or an upland site. Seed is collected site specific. Thesedifferent types of seed are referred to as ecotypes. Proper selectionresults in tree improvement, superior adaption to planting sites all ofwhich add to economic and aesthetic value.

Seed handling is also an important component in the acceleration of treegrowth. Collected seed are processed by cleaning out any foreignmaterials. They are then processed through an aspirator to separate outthe heaviest individual seed. Density is the most important factor ingermination capacity of any seed, and survival of the seedling. Densityis a measure of the stored food reserve. After the heaviest seed areselected they are then processed through a sieve which grades them bysize, e.g. three (3) or four (4) different sizes. Only the largest,heaviest seed are used. Since these factors (weight, size, and density)are genetic in nature these processes have definite effects on thegenetic improvement of the progeny.

Seed stratification and timing are also important in the acceleration oftree growth. The length of time required for stratification ispredetermined so germination can start (For example February 1st.) Thusthe seed must be handled in such a manor that all stratificationrequirements are satisfied prior to February 1st. Thus, for example, aseed requiring ninety (90) days of cold stratification would have to beplaced in our cold storage November 1st, so that it could be germinatedby February 1st. As shown in FIGS. 5 and 6, the seed is preferablypre-sown in the stratification media (which is preferably the same asgrowing medium, described below) and as shown in FIGS. 7, 8 and 9, theseeded trays are stacked in a cold storage room where temperature ismaintained at 32 F°. The seed are placed on the surface of the growingmedium. When germination begins, the outer seed coat splits exposing theseed cotyledons. When exposed to light the cotyledons turn from theirnormal pure white to green, indicating they are photosynthesizing andproducing additional energy for the germinating seedling. The inventors'research shows that most of the energy produced by the seed's cotyledonsgoes to the production of the plants root system, thus adding to theprimary goal of producing and enhancing an improved root system. This isin contrast to the established conventional rule that the depth of seedplanting should be twice the diameter of the seed. The 32 F.°temperature will prevent pre-germination of seed once its ripeningrequirements have been satisfied. This 32 F.° temperature is also incontrast to the established convention wisdom of temperatures betweenabout 37 F.° to 41 F°. Still another difference from conventionalmethods is placing the seeds in growing media. Historically seeds havebeen stratified separately and then seeded immediately prior togerminating.

The timing of the above steps in the method is based on having theseedlings processed through termination, Step I root pruning, grading,and Step II transplanting, so they are ready for planting outdoors bythe frost free date (approximately May 10 in Missouri). This gives theseedlings the maximum growing period until the first fall frost,approximately 210 growing days. A time sequence might be: February1st—start germination in greenhouse at a temperature of between 68 F.°and 72 F.° for about thirty days, as shown in FIG. 10. March 1sttransplant to square deep bottomless containers for additional airpruning of the lateral roots produced in the seed flat pruning.Containers 2¾×2¾×3 inch have been used satisfactorily for this step, butthe inventors have determined that containers 3 9/16×3 9/16×4¼ inchproduce superior plants as shown in FIG. 30. At the end of Step II, theseedlings are between 12 inches and 18 inches in height and are ready tobe planted in their final growing container outside in a nurseryproduction area.

As described above, the seeding is done by placing seed on a bottomlessmesh seed flat. While seed flats measuring 18½ inches×14½ inches×2½inches deep with mesh spacing of ⅜ inches have been used satisfactorily,as shown in FIG. 29, seed flats measuring 15¾ inches×15¾ inches×5 inchesdeep with mesh spacing of ⅜ inches (FIG. 4) have been found to beoptimum. A soil-less seeding medium and growing medium is preferablyused. The seeding medium consists of 40% composted rice hulls, 40% pinebark, 20% sand, which results in a desirable 35% air space has been usedsatisfactorily, but a medium of 35% composted rice hulls, 35% pine bark,20% sand, and 10% manure, which results in a desirable 35% air space hasbeen found to be optimum. A complete slow release fertilizer plusmicro-nutrients and a wetting agent are added to the medium. The growingmedium is also inoculated with mycorrhizae spores which germinate andgrow on and inside the tree roots in a symbiotic relationship (see FIG.23). Research has proven these fungi play an extremely importantfunction on trees. They provide an immune system for the trees, blockinginfectious diseases. They form such a dense mass they are able toenhance the capability of the root surface up to 1,000 times furtherenhancing the uptake of moisture, nutrients, and air resulting in aplant that can withstand greater stress situations and still perform andgrow, displaying exceptional vigor.

There is a universal problem of proper nutrient uptake by woody plantsin artificial (soil-less) growing media. Through analysis of the mediacompared to the analysis of the leaves from plants grown in media forQuercus bicolor—Swamp White Oak, the inventors have determined that theaddition of 10% composted manure to the growing media of composted ricehulls, pine bark, and sand plus slow release fertilizer and minor tracenutrient improves the nutrient level in the plants, with most of thenutrients moving from a low interpretation in the soil medium to adesired level within the plant resulting in maximum plant growth andperformance.

The addition of manure promotes the development of a balanced biologicalatmosphere within the growing media, promoting the growth of numerousbeneficial organisms. These organisms help promote the development ofdesirable soil fauna that break down organic matter releasing essentialbi-products (enzymes etc.) that benefit the plant by enabling uptake ofnutrients that are present in the media here-to-fore but not availablein a form the plant can absorb. This resulted in a reduced fertilizerrate of 50%, resulting in substantial cost savings. Also there is lessimpact on the environment because of fewer nutrients leaching and runoff while still achieving maximum plant growth.

The inventors have also discovered that the incorporation of ¾ of apound of Talstar systemic insecticide in each cubic yard of growingmedia trans locates throughout the plants system, helps plants grown inthe media to ward off attack by a number of undesirable insect pestsincluding but not limited to Japanese beetle.

As shown in FIGS. 10 and 11, in the first air-pruning step, seeded flatsare placed on raised greenhouse benches with air circulating beneath thebenches. As germination of the seed begins to occur in theabove-described bottomless flat, the following sequence occurs. Theseedling radical (tap root) penetrates down through the media andemerges through the ⅜ inch mesh, coming into contact with aircirculating beneath the raised bench (see FIG. 12). The root tip iskilled (dried) by the air, at a depth of 3 inches. Compare FIG. 37,showing a conventionally grown pecan seedling, with FIG. 36 showing apecan seedling grown in accordance with the principles of the presentinvention. The shallow air pruning achieved with the method of thepresent invention induces rapid lateral root development high (wheremost desired) on the tree root collar where their function to thewelfare of the tree will be best served.

This root pruning preferably occurs at about 2½-3 inches. Extensiveresearch conducted by the inventors has established that the ideal depthfor the first air root pruning (FIGS. 31 and 32) is about 3 inches.

As shown in FIG. 30, in the second air-pruning step, graded seedlingsare transplanted into a bottomless band measuring 3 9/16×3 9/16×4¼inches. This size band has been found to give improved growth andimproves the root distribution in the production container. The Step IItransplanted seedling bottomless bands are placed on raised bottomlessbenches to promote additional air pruning, which occurs on secondarylateral roots further enhancing the development of a shallow dense rootmass with many root tips. The first two steps are timed so the bands areready to be transplanted outside in the container production area duringearly May to avoid late frosts, but timed to take advantage of a fullgrowing season. Timing is further important because if properly handledit can coincide with the tree setting a temporary terminal bud. Whenthis occurs, photosynthate is trans located from the leaves down to theroots. This promotes very active root development, thus quickestablishment in the container area resulting in accelerated growth.

The inventors' research also determined that the optimum size of thecontainer for Step II is a bottomless tree band measuring 3 9/16inches×3 9/16 inches×4¼ inches deep (see FIG. 30) produces the idealroot mass to top (all of plant above soil) ratio.

BOTTOMLESS BANDS TESTED Band Size 1¼ × 1¼ × 3¾ 2½ × 2½ × 3¾ 2¾ × 2¾ × 5½3 9/16 × 3 9/16 × 4¼

This shallow air pruning is unique to the method of this invention, andenhances the root system resulting in the production of a superior plantthat can survive, perform, and grow faster under every condition tested.Prior root pruning methods typically prune at least 5 inches or more.The shallower air pruning of the present invention induces rapid lateralroot development high on the tree root collar, where most desirable, andwhere their function to the welfare of the tree will be best served.

The inventors have also tested various bench heights (i.e., the heightfrom the greenhouse floor to the wire mesh supports) under a strictlycontrolled greenhouse environment, for both the first and second airroot pruning steps. Heights of 12, 18, 24, 30, and 36 inches were allcarefully tested. While there was little differences in the 30 and 36inches bench heights, both were far superior in air flow and subsequentroot pruning to 12, 18, and 24 inches. As a result, the inventors havedetermined that balancing effectiveness of root pruning versusconstruction and installation costs, and ergonomic considerations, aheight of 30 inches is optimum.

The seedlings are graded to identify the genetically superiorindividuals. Experience and research has proven that selecting thelargest seedlings after their first flush of growth identifies thoseindividuals that will remain dominant, grow faster, and exhibit geneticsuperiority when grown to a larger size and eventually out planted. Whengrading, particular attention is given to the combination of height,caliper, and root development. On most species of woody plants the top50% are retained and transplanted and the remaining plants arediscarded. This grading process has proven to be a significant step intree improvement.

The graded seedlings are then transplanted into a bottomless bandmeasuring 2⅞″×2⅞″×3¾″ in depth. (This short band gives improved growthand improves the root distribution in the production container.) Thetransplanted seedlings in the bottomless bands are placed on raisedbottomless benches to promote additional air pruning, which occurs onsecondary lateral roots further enhancing the development of a shallowdense root mass with many root tips. The first two steps are timed sothe plants are ready to be transplanted outside in the containerproduction area immediately after the last frost date (early May inMissouri) to avoid late frosts, but timed to maximize the growingseason. It is also desirable to coordinate transplantation outside withthe tree's setting a temporary terminal bud. When this occurs,photosynthate is trans-located from the leaves down to the roots. Thispromotes very active root development, and thus quick establishment inthe container resulting in accelerated growth.

As shown in FIG. 16, while in the greenhouse, the bands are preferablycontained in bottomless flats each holding 25 tree bands. When preparingto transplant out of doors plants must be handled in a special manner tomake the proper transition from a controlled greenhouse environment to amore stressful outdoor environment. The greenhouse process conditionsthe stomata (openings on the underside of the leaf) to lose theirelasticity and they are unable to narrow or close and controltranspiration (water loss) and the cuticle, a waxy layer that forms onthe leaf surface and protects the leaves has not formed. Both of theseconditions correct themselves in 48 hours when placed outdoors in fullsunlight. During this period they are intermittently misted to relievestress while becoming acclimated. After becoming acclimated they aremoved to a container production area (see FIG. 20), and transplantedinto existing pre-filled containers (see FIG. 19). A shallow widegrowing container is used, because most of the feeder roots remain inthe upper six to eight inches of soil after out-planting. The growingcontainer measures 10 inches across and 7 inches deep (see FIG. 19).This allows 25% more lateral root development than a smaller sizepreviously used. This production system results in growth to amarketable size in one growing season of approximately 210 days fromdate of seed germination (see FIG. 21).

As shown in FIG. 22, the root mass achieved with the methods of thepresent invention eliminates losses often experienced usingconventionally grown trees, especially those recognized to be difficultto transplant, such as Oak, Hickories, Ash, and Nut Trees. Using themethods of this invention, the inventors have achieved consistentsurvival rates greater than 95%, even at very stressful sites such aswetlands, (where flooding occurs), mine reclamation sites, andconstruction sites.

The trees produced with the method of this invention grow an average ofthree times faster than conventionally grown seedlings. As show in FIGS.24, 25, and 26, even after 15 years, the trees grow at 3 times the rateof conventionally produced trees. This accelerated growth rate greatlyincreases the value and economics of tree farming. Using the methods ofthis invention, the rate of turnover in most tree production could beincreased by 50% or more and make tree farming a profitable and viablegrowing enterprise.

Most varieties of trees grown under this production system haveexhibited early flowering and fruiting characteristics. Examples areSwamp White Oak (Quercus bicolor) and Bur Oak (Quercus macrocarpa). Itis generally accepted in the literature that these species beginflowering and fruiting at about 20 to 25 years of age. See, Schopmeyer,Seeds of Wood Plants in the United States, Agriculture Handbook No. 450,Forest Service, U.S. Department of Agriculture, Washington, D.C., Table2 (1974), incorporated herein by reference. However, as shown in FIGS.27 and 28 trees of these species grown in accordance with the methods ofthe present invention have consistently produced fruit in the 3rd yearafter out-planting. The inventors believe that these plants have as manyroot tips (where the hormones are produced) as naturally grown 20 to 25year old trees. This fast fruiting is very valuable from a regenerationand wildlife food standpoint. The inventors' research indicates thissame response occurs in both nut trees and fruit trees, specificallypecans, walnuts and apples.

Specific differences between the method of the present invention, andprior methods of tree production include: (1) the shallow depth of airpruning (about 2½″); (2) seed grading to select genetically superiorseeds; (3) transplantation after the first root pruning to bottomlessbands to further increase root mass, as shown in FIGS. 16, 17, and 28;(4) the shallow depth of the bottomless band compared to conventionaldeeper containers that accommodated the tap roots 3 9/16 inches×3 9/16inches×4¼ inches; (5) the growing medium (see FIG. 19) that combines theproper amounts of air, nutrients, and beneficial natural soil bornorganisms in balance with an enhanced root system that properly utilizesand assimilates them, the result is greatly accelerated growth ratesthat persists for years; (6) high transplantability and survival oftrees produced with the method of this invention, which is nearly 100%survival when out-planted under virtually all conditions, and greaterthan 95% plus on stressed sites where conventional produced seedlingssurvived at rates of 2% or less. Sites tested include wetlands that arerepeatedly flooded, strip mine reclamation, and other problem plantingsites and conditions.

The inventors have propagated approximately 750,000 containerized oakand nut tree seedlings per year, many of which have been out-planted onabandoned mine lands, old wetland sites and fields in central andwestern Missouri. First-year establishment success for containerizedseedlings is approximately twice the success of bare-root seedlings inside-by-side field trials. Greatest mortality resulted from excessivecompeting vegetation and rodent damage in winter. Tap-rooted hardwoodssuch as oak, hickory, and walnut responded well to air-pruning, whichresulted from using bottomless containers. Seedlings were propagated andplaced upon a raised, welded hog or cattle panel, with four-inchsquares, protected from squirrels by a wood frame and chicken wire.

Qualitative observation of establishment success suggests a first-seasonsurvival rate of 90 percent for air-pruned bur oak and pecan grown inhalf-gallon bottomless containers. This compares to 40 to 50 percentsurvival of year old bare-root stock grown at a local nursery. Thesewere side-by-side trials of seedlings planted in prepared rows ofprairie soils in Conservation Reserve Program (CRP) crop fields inwestern Missouri. Rows were set at 15-foot centers, disked, and plantedby hand. Containerized seedlings were planted in fall, and bare-rootseedlings were planted in spring. Success rates were slightly higher invery fine sandy loam soils mapped as Bates loam, (2 to 5 percent slopes,fine-loamy, siliceous, therrvic (Typic Argiudolls) compared to siltyclay soils mapped as Kenoma (2 to 5 percent slopes, fine,montmorillinitic, thermic Vertic Argiudolls) (USDA 1995). Competitionbecame intense in mid-summer as late-season weeds such as common andgiant ragweed; cocklebur and begger ticks germinated from the old-fieldseedbank. The rows were mowed in July to prevent shading of theseedlings.

A second test plot was established on rough-graded, neutral mine spoils(silty clay texture with 15 percent shale channers, 5 percent sandstonepebbles and few sandstone cobbles) in western Missouri. Establishmentsuccess in the first season was approximately 75 percent forcontainerized bur oak and pecan compared to 30 percent for bare-rootseedlings. Compaction was minimal since all grading was performed by aD-3 dozer knocking the tops off the spoil-ridges, pushing the fill intothe valleys between ridges. Wind-disseminated species, particularlybroomsedge, slowly colonized the plots, competing with the seedlings.Adjacent mine spoils were heavily vegetated, enabling deer to browse theplot undisturbed.

A third test plot was established in central Missouri on loess-derivedforest soils that had been cleared in the 19th century, farmed andplanted to tall fescue in recent decades. In places, much of the Ahorizon had been eroded and mixed by plowing into the E horizon. Thesoils were classified as eroded Winfield silt roam (fine-silty mixedmesic. Typic Hapludalfs) (USDA 1994). Fescue sod was removed with aheavy hoe around each seedling to reduce competition at the time ofestablishment. Spraying also is effective; but the seedlings should bedormant. First-year success rates for containerized bur and northern redoak were 90 percent compared to 25 percent for bare-root.

The following table shows a hypothetical cost/benefit analysis of plantsgrown in accordance with the principles of the present invention versusconventional bare root plants.

HYPOTHETICAL COST/BENEFIT, SURVIVAL AND ENHANCED GROWTH RATE COMPARISONBETWEEN SEEDLINGS GROWN IN ACCORDANCE WITH THE PRESENT INVENTION ANDBARE ROOT SEEDLING OAK TREES BARE BARE BARE INVENTION INVENTIONDESCRIPTION ROOT 1 ROOT 2 ROOT 3 (UPLAND) (DOWNLAND) SURVIVAL 85% 50%30% 90% 90% RATE Cost per 1000 $500 $500 $500 $7500 $7500 plantedSurvival per 850 500 300 900 900 1000 planted Years of fruit 0 0 0 10 10production Pounds of 0 0 0 36,000 36.000 fruit production Carbohydrate 00 0 14,398 14,398 value (based on corn) Average dhb 16 inches 16 inches16 inches 20 inches 24 inches Wood fiber 81 brd ft. 81 brd ft. 81 brdft. 170 brd ft.  260 brd ft.  yield per tree Total Volume 68,850 40,50024,300 153,000 234,000 of wood fiber Value per $20,655 $12,150 $7,290$45,900 $70,200 1000 planted @ 0.30/brd ft. Value of early 0 0 0 $14,398$14,398 fruiting Total value $20,655 $12,150 $7,290 $60,298 $84,598 Cost$500 $500 $500 $7500 $7500 Gross Return $20,155 $11,650 $6,790 $52,798$77,098

What is claimed is:
 1. A method of facilitating air root pruning ofseedlings, the method comprising: placing seeds on a surface of agrowing medium; germinating the seeds on the surface of the growingmedium to obtain seedlings; subjecting the seedlings to a first air rootpruning by growing the seedlings in a first bottomless container of 2½inches to 3 inches deep; and after the first air root pruning,subjecting the seedlings to a second air root pruning by growing theseedlings in a second bottomless container of 3 inches to 4¼ inchesdeep.
 2. The method according to claim 1, wherein the growing mediumcomprises 35% to 40% composted rice hulls and 35% to 40% pine bark. 3.The method according to claim 1, wherein the air root pruning of theroots of the seedlings is performed by the growing medium being in oneor more containers having an open bottom, the one or more containersadapted to be set on a mesh support.
 4. The method according to claim 3,wherein the open bottom and mesh support are configured to expose to airat least some roots of the seedlings growing in the one or morecontainers.
 5. The method according to claim 1, further comprisingstratifying the seeds on the growing medium at 32 degrees F. prior tothe seeds germinating.